1. Field of the Invention
The present invention relates to a nozzle plate which is to constitute a part of a print head of an ink-jet printer capable of ejecting an ink toward a print media so as to form a desired image on the print media.
2. Discussion of Related Art
There is known an ink-jet print head which is constituted by a plurality of thin plates which are laminated on and bonded to one another. Each of the laminated thin plates has apertures formed by, for example, an etching operation, so that the apertures formed in the laminated thin plates are mutually connected and cooperate with one another to form pressure chambers, manifold chambers, communication passages and nozzle holes within a laminated structure provided by the laminated thin plates. The ink-jet print head constituted by the laminated thin plates includes a head body and a nozzle plate which is bonded to a surface of the head body. The head body has the pressure chambers in each of which the ink is pressurized by activation of a piezoelectric element, and the communication passages for supplying the ink from the pressure chambers toward the nozzle holes. The nozzle plate has the nozzle holes through which the ink is ejected toward the print media. This ink-jet print head is capable of ejecting, through the nozzle holes, the ink in the form of fine droplets toward the print media at a high speed.
It is known that the nozzle plate may be coated at its outside surface (which is to be opposed to the print media) with a plating layer having a non-wetting characteristic, in the interest of preventing the ejected ink from adhering to the nozzle plate.
For assuring a reliable prevention of the ejected ink from adhering to the nozzle plate, it is desirable that the plating layer is adapted to cover the entirety of the outside surface of the nozzle plate including an edge of opening of each of nozzle holes, for thereby preventing the ink from adhering to the edge of the opening of each nozzle hole. However, it is difficult to control the plating operation in such a manner that enables the plating layer to be formed to extend up to the edge of the opening of each nozzle hole. Particularly, where the diameter and density of the nozzle holes are reduced and increased, respectively, for satisfying recent demands for a further improved quality of printed images, it is extremely difficult to enable the plating layer to be formed to extend up to the edge of the opening of each nozzle hole.
There is known an arrangement in which the plating layer is intentionally extended to the inner surface of each nozzle hole so that the inner surface of each nozzle hole as well as the outside surface of the nozzle plate is covered by the plating layer. This arrangement is effective to prevent the ejected ink from adhering to the edge of the opening of each nozzle hole. However, this arrangement suffers from a reduced degree of wettability (affinity) of the inner surface of each nozzle hole with respect to the ink, because the inner surface of each nozzle hole is coated with the plating layer having the non-wetting characteristic. The reduced degree of wettability of the inner surface of the nozzle hole makes it difficult to reliably form a desired-shaped meniscus (curved free surface) of the ink at the opening of each nozzle hole.
For achieving a printing operation with an ink-jet printer at a high accuracy, it is necessary to appropriately control a shape of the meniscus formed at the opening of each nozzle hole. This is because a direction of ejection of the ink droplet and a size of the ejected ink droplet vary depending on the shape of the meniscus. In this sense, there has been developed various techniques for forming the nozzle plate with a high precision, for obtaining an appropriate shape of the meniscus, and accordingly for improving the performance of the ink-jet printer.
As a technique for forming the nozzle hole in the nozzle plate, there is known a process including a step of piercing the nozzle plate by using a punch which has a generally conical shape configured to form a desired shape of the nozzle hole. Described more specifically, a portion of the nozzle plate (in which the nozzle hole is to be formed) is plastically deformed by the punch in a direction away from the inside surface of the nozzle plate toward the outside surface of the nozzle plate, such that a recess and a protrusion are formed in the inside and outside surfaces of the deformed portion of the nozzle plate, respectively. Then, the protrusion formed in the outside surface of the plate is eliminated in a polishing operation with abrasive grains, so that the recess formed in the inside surface of the plate converts into a through-hole as the nozzle hole. An example of this process is disclosed by JP-A-2000-289211.
As a technique for forming the non-wetting plating layer, there is known a process including a step of a masking step of masking the inside surface of the nozzle plate and the inner surface of each nozzle hole, and a non-wetting-layer forming step of forming the non-wetting plating layer on the outside surface of the nozzle plate. Described more specifically, in the masking step, a resin is provided to cover the inside surface of the nozzle plate and a tapered portion of the inner surface of each nozzle hole, so that the outside surface of the nozzle plate and a small-diameter end portion of the inner surface of each nozzle hole (which portion is adjacent to the outside surface of the nozzle plate) remains unmasked. In the non-wetting-layer forming step, the non-wetting plating layer is formed to cover the outside surface of the nozzle plate and the small-diameter end portion of the inner surface of each nozzle hole which are not masked with the resin. An example of this process is disclosed by JP-A-2001-18398.
As another technique for forming the non-wetting plating layer, there is known a process including a wetting-layer forming step of forming a wetting layer (made of a material having a wetting characteristic) on the inside surface of the nozzle plate, and a non-wetting layer forming step of forming the non-wetting layer on the outside surface of the nozzle plate and an end portion of the inner surface of each nozzle which portion is adjacent to the outside surface of the nozzle plate. In the non-wetting-layer forming step, the wetting layer serves as a masking member, so that the non-wetting layer is not deposited on the inside surface of the nozzle plate which is covered with the wetting layer. An example of this process is disclosed by JP-A-H9-85956.
However, in the above-described known techniques for the formation of the non-wetting layer, the non-wetting layer can not be formed accurately on a required area of the nozzle plate, because of difficulty in covering accurately the required portion of the inner surface of the nozzle hole with the resin, or in forming the wetting layer as the masking member accurately on the inside surface of the nozzle plate. That is, in the known techniques, it is difficult to stably establish a desired boundary between the wetting area and the non-wetting area in each nozzle hole, making it impossible to provide each nozzle hole with a desired characteristic of ink ejection.